French Drain Calculator
Enter your trench length, width, and depth to estimate the drainage gravel in cubic yards and tons and the length of perforated pipe needed for a French drain.
Results
- Drainage gravel
- 3.06 cu yd
- Estimated weight
- 4.28 tons
- Perforated pipe
- 50 ft
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
Enter your trench length, width, and depth to estimate the drainage gravel in cubic yards and tons and the length of perforated pipe needed for a French drain.
How to use the french drain calculator
- Enter the trench length in ft.
- Enter the trench width in in.
- Enter the trench depth in in.
- Enter the waste factor in %.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Trench length
- 50 ft
- Trench width
- 12 in
- Trench depth
- 18 in
- Waste factor
- 10 %
Results
- Drainage gravel
- 3.06 cu yd
- Estimated weight
- 4.28 tons
- Perforated pipe
- 50 ft
Using the example values above, the french drain calculator returns 3.06 cu yd (drainage gravel). Change any field to match your own project and the numbers update instantly.
How much extra should I order?
Always order a little extra. A 5% waste factor suits simple, square projects; 10% is right for most jobs; bump it to 15–20% for irregular shapes, diagonal patterns, or uneven ground. Running short almost always costs more than the leftover material.
Formula
Gravel volume = length × width × depth. Cubic yards = volume ÷ 27. Tons = cubic yards × 1.4. Pipe length = trench length.
Frequently asked questions
- What gravel is best for a French drain?
- Use clean, washed 3/4-inch crushed stone or river rock so water flows freely and fines do not clog the drain.
- How deep should a French drain be?
- Most French drains are 12–24 inches deep and 6–12 inches wide, sloped at least 1% (1 inch per 10 feet) toward the outlet.
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